B. Protein Blotting

A general protocol for sample preparation.

Lyse cells by adding 1X SDS sample buffer (100 µl per well of 6-well plate or 500 µl for a 10 cm diameter plate). Immediately scrape the cells off the plate and transfer the extract to a microcentrifuge tube. Keep on ice.

Western Blot Reprobing Protocol

Reprobing of an existing membrane is a convenient means to immunoblot for multiple proteins independently when only a limited amount of sample is available. It should be noted that for the best possible results a fresh blot is always recommended. Reprobing can be a valuable method but with each reprobing of a blot there is potential for increased background signal. Additionally, it is recommended that you verify the removal of the first antibody complex prior to reprobing so that signal attributed to binding of the new antibody is not leftover signal from the first immunoblotting experiment. This can be done by re-exposing the blot to ECL reagents and making sure there is no signal prior to adding the next primary antibody.

(Optional) To assure that the original signal is removed, wash membrane twice for 5 min each with 10 ml of TBST. Incubate membrane with LumiGLO® with gentle agitation for 1 min at room temperature. Drain membrane of excess developing solution. Do not let dry. Wrap in plastic wrap and expose to x-ray film.

Wash membrane again four times for 5 min each in TBST.

The membrane is now ready to reuse. Start detection at the "Membrane Blocking and Antibody Incubations" step in the Western Immunoblotting Protocol.

Source / Purification

Background

The Rho family of small GTPases, including Rho, Rac, and Cdc42, act as molecular switches that regulate processes such as cell migration, adhesion, proliferation, and differentiation. They are activated by guanine nucleotide exchange factors (GEFs), which catalyze the exchange of bound GDP for GTP, and inhibited by GTPase activating proteins (GAPs), which catalyze the hydrolysis of GTP to GDP (1). The serine- and proline-rich GAP protein, Cdc42 GAP (CdGAP), has been shown to be a negative regulator of both Cdc42 and Rac1, but not RhoA (2,3). This protein contains three domains: an amino-terminal GAP domain, a central domain, and a carboxy-terminal proline-rich domain containing five Src homology 3 (SH3)-binding sites. It is suggested that threonine and serine phosphorylation within the proline-rich domain likely alters protein-protein interactions and determines the localization of CdGAP (4). Phosphorylation of CdGAP on threonine 776 by both ERK-1 and GSK-3 has been shown to negatively regulate protein activity, possibly by inducing a conformational change within the protein disrupting its ability to bind SH3 domains (4,5). Upregulation of CdGAP has been shown to increase cell proliferation and it has been suggested that this protein may play a role in TGF-β-induced cell growth, motility, and invasion in some breast cancer cells (6).